(a) Field of the Invention
The present invention relates to an organic light emitting device (OLED) and its manufacturing method.
(b) Description of the Related Art
Recently, as demand for light and thin monitors or televisions has been increasing, cathode ray tubes (CRTs) are gradually being replaced by liquid crystal displays (LCD).
While LCDs have numerous advantages over CRTs, it is not without shortcomings. For example, because an LCD is a non-emissive element, it requires a light source (usually in the form of a backlight). Furthermore, an LCD's response speed and viewing angle are not always ideal.
In search for a display device that does not share the problems LCDs have, OLED is receiving much attention.
An OLED includes pixel electrodes, a common electrode, and an emission layer positioned between the pixel electrodes and the common electrode. In the OLED, electrons injected from the common electrode and holes injected from the pixel electrodes combine in the emission layer to form excitons, and as the excitons discharge energy, the OLED generates light. Because an OLED does not require a light source, it is advantageous in terms of power consumption. Furthermore, an OLED has good response speed, viewing angle, and contrast ratio compared to LCDs.
OLEDs can be divided into passive OLEDs and active OLEDs depending on the driving method. In an active OLED, pixels are driven by using thin film transistors (TFTs) as switching elements and driving elements. An active OLED has advantages such as high resolution, low power consumption, and the possibility of a large area.
In order to enhance the luminance of an OLED and increase the luminous power per unit pixel, a method for enhancing the efficiency of a luminescent material and a method for increasing electrical current applied to each pixel electrode can be considered. However, there are practical limitations in the development of a luminescent material of high efficiency, and the method for increasing the amount of current applied to the unit pixel electrodes also has a limitation with respect to life span and efficiency of the OLED and a life span of TFTs.